Exchange
by dragondark
Summary: Roxas needs to escape and the Doctor needs somebody to save. Doctor Who crossover.


**Author's Note: **Written about two years too late and just about to be Jossed in the most official way possible, but hey. Ten meets Roxas. Set just before season three of Doctor Who and just after Roxas leaves the Organization in KHII. 1261 words.  
**Disclaimer:** Do love, do want, but do not own. Woe.

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**Exchange**

"You haven't got a heart," he says - rather foolishly, he realises in retrospect.

Roxas only says, "No," and looks about the TARDIS in a way the Doctor hasn't seen in quite a while. He's gotten used to humans with their blithe and endless practicality about everything, to beings who would take one look at a controlboard as complex and full of dials as the TARDIS's and say something like, "So, does it do chips, too?"

Not that the boy isn't human. The scans have told him that, in point of fact, he is: DNA a hundred percent what it should be. "But no human should be able to manipulate the darkness like that," he murmurs. "That's like - that's like _magic_. Of course," he adds, scratching his head and eyeing his new passenger for signs of unexpected tentacles, "there was that one colony in the sector of--"

"We should go," Roxas says. He drifts towards the wall farthest from the door, shoulders set and narrow. "They nearly caught up back there."

"Ah -- yes! Of course!" And suddenly the Doctor is in motion. Anomalies or not, the constant remains: the TARDIS, old and dear, capable of everything. He yanks handles, flicks dials, presses button after button until the voyage path runs clear. On cue, they hear the familiar whirr roar into life. "Now," he says while the TARDIS spins off into space, "did you happen to mention _why_ they were after you in all that to-do?"

Roxas slants a look out of the corner of his eyes, and the Doctor recognizes this one, too - seen it before in flashes between heavy jungle vines; in the jeweled circlet of an emperor in the highest citadel; glittering out of a civilized man's eyes as he comes to a conclusion. It's a predator's glance, always watchful for the chance to overtake and overthrow. Probably Roxas doesn't even know that he does it. So many hunters are unaware that they're hunting, only that they can want and have in the same breath.

But it does make the Doctor wonder, a little, what he's brought into the TARDIS.

"This," Roxas says at last, breaking his trance. A sword shaped like a key flashes into being, and Roxas catches it easily.

"That--" The Doctor whips out his glasses and peers at the long, strange blade in Roxas' hand. He starts back, hands waving in protest as Roxas raises his arm, but realises that the boy's only adjusting his grip to let the Doctor have a better look. "Hmm. Thank you." In itself it's not a complex piece: it's what the laws of this particular universe allow it to do that makes it fascinating.

"Is it so bad," the boy says, "not having a heart?"

Surfacing out of mutters about continuum mathematics and engines, the Doctor says, somewhat distractedly, "What? Oh--" remembering his earlier question, "--well, I suppose it depends on your perspective. I've known some, of course, who wouldn't have wanted a heart if they thought that they could get away without one. What's it like for you?"

It's not an entirely scientific question, but he is curious. He can't help it. There's just something absorbing about a universe that lets you run around breathing and eating and doing all the little things that make one human without the major _human_ factor.

Roxas doesn't even consider the question. "Empty," he says. "We can't feel."

It sounds a bit melodramatic to him, and he'd know all about dramatics, considering he spent all of one lifetime with a vegetable pinned to his coat. "Can't you?" The Doctor reaches out and pinches him.

"Hey!" Caught off-guard, Roxas lets his eyes slit. Light glints off of the Keyblade in unsubtle menace. "What was that--"

"Feeling, wasn't it?"

"I mean emotions."

"Well, you felt annoyance just now, didn't you? Ah, there goes irritation, surprise, and a feeling describable only as "wanting to kick the other person in the trousers". I know a species that's invented a word for that, but it's out of your dimension, so I suspect that knowing it wouldn't do you any good." He clicks his glasses shut and tucks them into his breastpocket once more. "So, tell me. Why _are_ they chasing after that-- what d'you call it?"

"Keyblade."

"Oh, right."

"They need it," Roxas says. "They've got plans."

"Aha, plans. And you're out to foil them, I suppose?"

Roxas shakes his head in a way that suggests that a few signals crossed along the way and he wants to be nodding, or perhaps to be doing a wild tango with an elephant. Too volatile, too sharp, the world a mesh of furious edges-- It's been a long time since the Doctor was that young. "I just want to know why the Keyblade _chose _me."

"But that's not the kind of thing you can go looking for." Roxas only shakes his head again. "Right, then." The Doctor switches tactics. "Who're you going to ask?"

"I--"

"Don't just tell me that you were going to go wandering all around the worlds with a great big weapon capable of destroying entire _continents_ in your right hand."

"Left."

"What?"

"It's my left hand," Roxas points out. "And why do you care? You said you couldn't get involved."

The Doctor takes care to look vague. "Did I?"

"Time-traveling; someone you had to rescue; _one_ trip, you said."

"Well, then, that's brought us to a tricky bit, hasn't it?"

"How?"

"I can't just leave you here knowing that you'll probably blow up whatever place you land on with that thing. It wouldn't be right."

"You can't take it away," Roxas says with the careless confidence of power. The Keyblade shimmers and vanishes from his hand once more. "It always comes back to me."

"Who said anything about taking it away? And what good would a whopping key do me, anyway?"

Roxas shrugs. "Everyone has a door they want to open -- or close. The Keyblade does that."

His words sound familiar - not as if he's heard them before, but as if they fit into some piece of history that the Doctor hasn't quite grasped. He cocks his head, squinting at the air, tasting salt in his throat, and hears that jovial, long-ago voice saying, _There's one tiny little gap in the universe left, just about to close._

No.

_I'm burning up a sun just to say--_

It's a horrible idea. It's the worst idea in the universe, except it fits. It falls under all the laws of this universe and the other, because that's what the Keyblade _does_ - it opens ways between dimensions without damage. The TARDIS couldn't have done this. Nothing in the world - the other world, anyway - could have managed to piece together an engine that could have pierced the walls between universes without splintering all of time.

But the Keyblade can.

If they're quick and if they get it right, he could--

"See?" Roxas says, and the Doctor realises that his expression must have been transparent, brilliant with old ghosts. He shifts his weight and looks at the Doctor with perfect indifference - boy in a black coat with luminous, dying eyes. "You've thought of something."

It's an exchange, offered in words that aren't quite words. Roxas needs to escape; and the Doctor needs somebody to save. Yes, he thinks, and finally there's a solution that isn't selfish or precarious but just, finally, _simple_.

"Right," he says, swallowing down his dread to reach for the first dial that'll take them to the source. "_Allons-y!_"

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_beginning_

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**reviews:** are very cool.


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